Three-Axis Gasless Sounding Rocket Payload Attitude Control

Gas released by current sounding rocket payload attitude control systems (ACS) has the potential to interfere with some types of science instruments. A single-axis gasless ACS experiment was successfully flown on a sounding rocket. The single-axis system is being expanded to three axes to provide gasless attitude control with greater accuracy than is presently achievable.

Sounding rocket payload attitude is currently controlled by a system of cold gas thrusters. The gas released by the thruster has the potential to interfere with science instruments that are sensing matter in the local environment. There is interest in the sounding rocket science community in an ACS that can provide fine attitude control without releasing gas. A three-axis reaction wheel assembly (RWA) can provide gasless fine attitude control during science operations. Large maneuvers and coarse control would still be provided by the standard cold gas thrusters, but the gas would be shut off and control would be handed over to the RWA during portions of the flight critical to sensitive science instruments. In addition to being gasless, a RWA ACS can also provide more precise attitude control than can be achieved through pulsed thrusting of a cold gas system.

A single-axis gasless ACS proof of concept experiment was flown March 1, 2016.

The scope of the project is to expand the single-axis system used for the proof of concept flight into a three-axis ACS. Existing software for the controller and software-in-the-loop (SWIL) simulation testing will need to be expanded to include pitch and yaw axes. Maneuver limits and wheel saturation rates with typical disturbances will be estimated to create a trade space of hardware requirements, and hardware that meets those requirements will be identified. Potential processors will be evaluated. Wheels will be sized for the pitch and yaw axes and re-evaluated for the roll axis. Capability for spinning attitude control will also be added. Performance estimates will be made for both the LN-200 and the more accurate LN-251 IRU.

The overall objective of the project is to mature the three-axis design to the point that it will represent a minimal schedule risk when included in either a Sounding Rocket Program Office (SRPO) development mission or a science mission willing to take a risk on a developmental system, and to develop an accurate cost estimate to aid in securing funding for a flight demonstration. Project deliverables will include controller software for both spinning and non-spinning payloads, a set of hardware requirements for the system, and performance and cost estimates for the system.